Electric hair clippers and trimmers have a stationary blade and a reciprocating blade. In clippers containing a rotary electric motor the reciprocating blade is moved laterally back and forth over the stationary blade as a motor shaft turns a cam eccentric which is operatively connected to the reciprocating blade. The reciprocating blade and several associated pieces are assembled in the handle, and the stationary blade is placed over the reciprocating blade and secured to the handle by screws or the like. Installing or changing the blade assembly for servicing requires use of a special tool, such as a screw driver.
Some hair clippers have detachable blade assemblies which can be installed and removed without hand tools by securing the assembly to the handle of the clipper with snaps. The reciprocating blades in such assemblies can be held in place by wire tension springs which reciprocate with the blade, thereby creating minimal frictional loads on the motor. However, wire tension springs often do not provide accurate and rigid lateral guiding with respect to the stationary blade. The reciprocating blade can rotate to a degree, particularly under substantial cutting loads. This rotation can cause the points of the teeth of the reciprocating blade to move beyond the stationary blade and nick the skin.
Rotation of the blade can be prevented by securing the reciprocating blade with a heavier stationary metal tension spring as seen in U.S. Pat. No. 2,928,171 by J. Oster. However, because the stationary tension spring does not move with the reciprocating blade, this method of correction results in increased frictional resistance being placed on the motor, which is undesirable.
In the device of the present invention, rotation of the reciprocating blade has been reduced or eliminated by placing fixed blade guides adjacent each side of the stationary blade and installing a guide piece on the reciprocating blade. During operation, the cam eccentric rotates and moves the reciprocating blade and the guide piece through an operating stroke determined by the lateral distance the cam eccentric moves as it rotates. The guide piece is confined within the blade guides throughout the operating stroke so that the reciprocating blade can only move laterally. The reciprocating blade cannot rotate and is maintained parallel to the stationary blade, without substantially increasing the frictional resistance load on the motor.
When this type of blade assembly is detached from the clipper handle, such as for servicing, the reciprocating blade may be moved back and forth manually, to remove accumulated hair cuttings from the assembly. The reciprocating blade may also be moved in this manner if it is dropped when the assembly is detached from the handle. When moved manually, the reciprocating blade can travel through a distance which is longer than the operating stroke. Due to certain manufacturing and design constraints, explained below, it is possible for the guide piece to become disengaged from the blade guides when pushed far enough beyond one of the distal ends of the operating stroke. At this point the blade can rotate slightly, causing the guide piece to become locked against the edge of the blade guides. If the blade assembly is placed back on the handle in this condition, it will not operate.
For aesthetic reasons, it is preferably for the internal working of the blade assembly to be hidden by the solid side walls of the hair clipper case. Hair clippers are usually designed so that the case has dimensions which are as small as practical, but large enough to permit the reciprocating blade to move through its operating stroke without contacting the solid side walls of the case. In practice, the preferred case width has placed design constraints on the relative sizes of the guide piece, the blade guide and the stroke distance the reciprocating blade can travel within the handle. Due to these constraints, when the blade assembly is removed from the handle it is possible for the guide piece to be displaced from the blade guide when the guide piece is pushed beyond a distal end of the operating stroke of the reciprocating blade. The guide piece is then locked against the inside edge of the blade guide. In that event, the reciprocating blade cannot move back and forth, and when replaced on the handle, the clipper does not operate.
Thus, there is a need for blade assemblies for electric hair clippers having reciprocating blades fixed by a wire tension spring, which do not rotate under substantial cutting loads and can not be accidentally displaced out of their guide path and locked in an unmovable position when the blade assembly is removed from the handle and the reciprocating blade is pushed beyond a distal end of the operating stroke.
Accordingly, one object of this invention is to provide new and improved electric hair clippers.
Another object is to provide new and improved electric hair clippers or trimmers having blade assemblies which are easy to assembly and install, without the use of special tools.
Another object of this invention is to provide new and improved electric hair clippers which have accurate lateral guiding of the blade assembly while placing minimal frictional loads on the motor.
Still another object is to provide new and improved blade assemblies for electric hair clippers having accurate lateral guiding which cannot be accidentally displaced out of the blade guide when detached from the clipper and pushed beyond a distal end of the operating stroke.